Nanoscale experiments of intergranular dissolution-precipitation to understand deformation mechanisms in the upper crust.

In the upper crust, rock deformation commonly occurs in the presence of aqueous fluids, which are known to alter the material's response to stress. These fluids facilitate dissolution and precipitation, driving changes in the mineral composition and texture. The interaction between dissolution-precipitation and deformation in the upper crust has been studied in various natural geological cases, through experimentation, and modeling. Recently, there has been increased emphasis on understanding the role of fluids in deformation at the nanoscale. This experimental study aims to comprehend the effects of deformation on dissolution and precipitation at the nanoscale, specifically at the boundary between individual mineral grains.

Our research has focused on understanding quartz dissolution and precipitation at the grain boundary scale at hydrostatic pressures and temperature conditions representative of the upper 5 km of the crust. We report preliminary findings from our experiments on nano-milled quartz crystals, representing natural grain boundary geometry, in contact with different aqueous solutions in a closed system. The pH, salinity, and concentration of Si in solution were systematically altered to assess their impact on dissolution rates. By using ¹⁸O-doped solutions, coupled with nanoscale secondary ion mass spectrometry and atomic force microscopy, we can track the dissolved and re-precipitated material, and monitor the changes in the geometry of the nano-milled quartz surface. This constitutes the initial step in our effort to further explore and quantify the effects of differential stress at the grain boundary. Additionally, we present results from a pilot study designed to test how differential normal stress impacts asperity dissolution within quartz-quartz contacts. These experiments aim to improve our understanding of dissolution rates in relation to pressure solution, a significant deformation mechanism in sedimentary and fault rocks.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie initial training network (FluidNET) grant agreement no. 956125.